A current technique for performing an excisional biopsy of a non-palpable breast lesion that has been identified by mammogram or other method involves placement of a needle or guide wire (e.g., a "Kopanz wire"), with or without blue dye, to guide the surgeon to the lesion. The tip of the needle is generally placed directly in or as close as possible to the lesion. When larger or more complex lesions are encountered, two or more guide wires are sometimes placed at each edge of the lesion. The entry point of the needle through the skin of the breast is usually several centimeters from the lesion due to the logistics of needle placement. The surgeon does not cut along the shaft of the needle from the skin because the distance is too great. Instead, the surgeon must estimate where in the breast the lesion is located by making reference to the location of the needle.
This technique is not optimal. Due to the amorphous and highly pliable nature of certain tissue, e.g., breast tissue, it can be difficult to properly define the margins of tissue to be removed, both during and after insertion of the needle(s). Also, it is often difficult for the surgeon to detect the exact depth of the lesion based on the placement of the needles. For these reasons it is not uncommon that the biopsied tissue does not contain the mammographically positive specimen. In other cases, as a result of the difficulty of estimating the proper location of the boundaries of the volume of tissue to be removed, the lesion ends up being eccentrically positioned within the volume of tissue excised. This calls into question the adequacy of the margin of normal tissue surrounding the lesion. In still other cases, more normal tissue is removed than is required, which is disadvantageous in this era of tissue-conserving therapies.
Breast lesions are typically excised with a scalpel manipulated directly by the surgeon. With the current emphasis on breast conserving surgical therapies, the above-described procedure for removing a breast lesion is typically performed through a narrow opening in the skin created by slitting and then pulling apart the skin. It tends to be difficult to manipulate the scalpel within this opening so as to remove the desired volume of tissue. The amorphous, pliable nature of breast tissue exacerbates removal of such tissue inasmuch as application of force to the scalpel causes movement of the breast tissue relative to the opening in the skin.
Cryosurgery is a well-established technique used in the treatment of many conditions. Cryosurgery involves the use of a cryoprobe, which is a long, needle-like device that delivers cold to a piece of tissue, thereby destroying the tissue. Cryoprobes typically include an inner tube that delivers a fluid at very cold temperatures, e.g., liquid nitrogen, to an internal orifice positioned near the tip of the cryoprobe. The cold fluid is dispensed through the orifice into a return chamber in the interior of an outer tube surrounding the inner tube. An exemplary cryoprobe is disclosed in U.S. Pat. No. 5,108,390 to Potocky et al., which patent is incorporated herein by reference.
By inserting a cryoprobe into a tissue mass present in a piece of tissue and then activating the cryoprobe, a volume of tissue adjacent to the cryoprobe freezes. The frozen tissue volume can then be removed from the piece of tissue or can be allowed to remain in place for removal by normal bodily function. When freezing a piece of tissue it can be difficult to know when to stop the freezing process so that the frozen tissue volume is of the optimum size. Stopping the freezing process too early will result in the tissue volune being smaller than the tissue mass, with the consequence that all the tissue mass will not be removed. On the other hand, stopping the freezing process too late will result in the tissue volume being substantially larger than the tissue mass, with the consequence that too much healthy tissue will be frozen and removed.
To address this concern, the size of the tissue volume should be monitored during the freezing process. One approach is to monitor the size of the tissue volume using conventional imaging techniques, such as ultrasonic imaging or magnetic resonance imaging (MRI). One example of such approach is described in U.S. Pat. No. 5,531,742 to Barken, ("the '742 patent"), which discloses a surgical system and method of computer controlled cryosurgery that relies on MRI-generated image of the tissue to be frozen While ultrasound imaging and MRI are, in many cases, reasonably effective techniques for monitoring the freezing of tissue using a cryoprobe, they involve the use of expensi ve equipment, do not provide adequate guidance as to when a sufficiently large volume of tissue has been frozen and are logistically cumbersome. Also, in some cases effective imaging is impeded by the cryoprobe itself.
Another approach is advocated by ENDOcare Incorporated, of Irvinc, California, which markets cryoprobes (e.g., model no. CRYO-40) having a tip capable of measuring temperature. The approach involves inserting a plurality of such cryoprobes or temperature probes into a tissue portion to measure tissue temperature at select locations. However, this technique suffers from the disadvantage that the cryoprobes and temperature probes protrude from the skin above the tissue portion, thus interfering with the surgical removal of the frozen tissue volume. It would, therefore, be greatly advantageous to be able to monitor the growth of a freezing tissue volume in a piece of tissue without the use of devices such as cryoprobes or temperature probes that protrude from the tissue portion and without the use of complex imaging systems.
In animal research studies, it is known to obtain animal temperature through the use of a small sensor, also known as a transponder, that is implanted in the animal. Sensors of this type are described in U.S. Pat. Nos. 5,724,030, 5,481,262 and 5,252,962, each to Urbas et al. The sensors described therein provides animal temperature and identification information in an output signal that is received by a receiver system of the type described in U.S. Pat. Nos. 5,420,579, 5,262,772 and 5,250,944, each to Urbas et al. Apparently, a single working sensor is implanted in the animal at any one point in time, and the sensor is used only to obtain animal temperature and identification information. While this system is believed to function effectively for determining a single temperature within a given animal, it is not suitable for assessing a temperature distribution in a portion of human or animal tissue. This is because the system (i.e., sensor and receiver) described in the above-identified patents to Urbas et al. is believed to lack the ability to perform multiple interrogations of different sensors located in close proximity to one another to obtain the temperature data necessary to precisely determine a temperature distribution at the boundary of a rclatively small tissue volume. In particular the sensors described in the Urbas et al. patents are not believed to possess the structure and functionality necessary to permit individual sensors to compare an identification code in an interrogation signal provided by the receiver with a unique identification code stored in the sensor and provide temperature information only when the codes match.